The two most common operations in the practice of drafting are the scribing of lines of specific lengths along the horizontal and vertical axes of the drafting work or drawing being created. A horizontal line of a certain length is generally produced by first marking the end point of the line on the drafting work with the use of a drafting scale or ruler, and then scribing the line along the working edge of a T-square or horizontal bar. Similarly, a vertical line of a certain length is generally produced by placing a triangle on the T-square or horizontal bar to create the vertical axis, marking the end point of the vertical line with the use of a drafting scale held along the edge of the triangle, and then scribing the line along the working edge of the triangle. Similar steps are normally required to produce lines at an angle, such as 45 degrees, from the horizontal or vertical axes of the drafting work. While these methods are effective, they suffer the disadvantage of inefficiency resulting from the need to use more than one instrument, and to move back and forth from one instrument to the other to complete the operation.
The use of standard drafting triangles and T-squares or horizontal bars introduces additional disadvantages arising from the full contact between the relatively extensive surface area of the face of the triangles and the drawing surface, which tends to produce smearing of the work, and from obstruction of the work by normally opaque areas of the commonly used drafting tools. The full surface contact between drafting triangles and the drawing surface also gives rise to problems with graphite and eraser residue accumulations under the triangles and between the triangle edge and the T-square or horizontal bar.
Various approaches to solution of these problems have been attempted and are known in the prior art, but none of the approaches have fully addressed the combination of problems, and none have presented a coordinated solution. L-shaped drafting instruments are known in the art, as illustrated by British Patent No. 386,883 and French Patent No. 730,763, both of which include beveled edges and some form of graduated scale. Those instruments do not, however, address the problems of extensive contact with the drawing surface or of residue buildup.
French Patent No. 1,385,756 discloses the use of raised points on the face of a T-square or triangle to raise the instrument above the surface of the drafting work, which does alleviate certain of the normal disadvantages of the use of a triangular instrument, but the design stops short of a coordinated solution to the full scope of problems associated with a triangular instrument and to the inefficiencies of the use of more than one instrument to produce lines of specific lengths. The use of a handle extending outwardly from at least one face of a drafting instrument has also been previously proposed, as in U.S. Pat. No. 831,314, U.S. Pat. No. 699,738, and U.S. Pat. No. 2,364,529. These designs are useful in providing a means of more readily grasping the drafting instrument with which they are used, but again do not address the full scope of problems.
It is an object of the present invention to provide a fully coordinated and highly efficient instrument for the production of lines of specific lengths, while addressing and overcoming the disadvantages associated with the commonly used forms of drafting instruments.